Rotational overtravel stops often are crucial components of actuators used in environments where not only cost but also reliability, weight, size and simplicity are important. For example, where rotating actuators are used to adjust the flaps of an airplane wing, the reliability of the overtravel stops are crucial in order to prevent possible structural damage and also to prevent the flaps from being adjusted to an aerodynamically unstable position should there be a failure in the primary control for the actuator. Simplicity also is important as it helps to ensure the reliability of the stops. Of course, weight, size and power requirements also are obviously important factors with such actuators.
A number of overtravel stops have been developed in the prior art in an attempt to meet these crucial needs. For example, Pollock U.S. Pat. No. 2,902,876 and Rowley et al U.S. Pat. No. 2,837,925 disclose overtravel stops using two gear pairs with different gear ratios, one gear being on a threaded shaft and translating over that shaft, such that stops at either end of the translation are engaged to stop the main shaft. Lee U.S. Pat. No. 2,502,573 similarly uses two gear pairs having different gear ratios, where translation of one of the gears operates a device disconnecting the drive motor.
Krell U.S. Pat. No. 2,620,911 and House et al U.S. Pat. No. 4,064,981 illustrate another type of overtravel stop which uses friction brake members which are biased together at either limit of travel. These stops often require more space and weight than is desirable in those applications wherein the travel limits are separated by several thousand revolutions.
In copending application Ser. No. 804,387, now U.S. Pat. No. 4,641,737 filed Dec. 4, 1985, and assigned to the assignee of this invention, an overtravel stop for a rotating shaft is disclosed and includes a fixed stop and a stop member about the shaft and adapted for axial motion thereon to engage the fixed stop. A cam structure is provided to axially move the stop member into engagement with the fixed stop when a travel limit of the shaft is reached. The cam structure is actuated to axially move the stop member in response to rotational shifting of the member relative to the shaft. In one aspect of that invention, the rotational shifting is accomplished by the use of two gear pairs having different gear ratios where one set of corresponding gears in the different pairs rotate together within the shaft travel limits, causing different relative rotation of the other two gears until the travel limits are reached. In another aspect of that invention, a cam structure comprises a pin and slot connection between the stop member and the shaft, or between the stop member and one of the gears.
The overtravel stop of the above-identified application has proven effective, and the present invention is directed to further improvements on such an overtravel stop.